Siemens IEEE802.11 Manual do Utilizador descarregar pdf (Página 43)

WLAN-IEEE802.11 Tutorial (Maximilian Riegel), 021018-wlan-tutorial.ppt Page 43 © Siemens, 2002

Time Axis

Beacon Interval

XXXX

"Actual time" stamp in Beacon

Beacon

Busy Medium

Infrastructure Beacon Generation

n APs send Beacons in infrastructure networks.

n Beacons scheduled at Beacon Interval.

n Transmission may be delayed by CSMA deferral.

– subsequent transmissions at expected Beacon Interval

– not relative to last Beacon transmission

– next Beacon sent at Target Beacon Transmission Time

n Timestamp contains timer value at transmit time.

1 2 ... 38 39 40 41 42 43 44 45 46 47 48 ... 83 84

Maximilian Riegel 1
The ubiquitous WLAN 2
WLAN has taken off 3
Part 1: 5
Internet/Web Applications 6
Layering means encapsulation 7
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IP based network architecture 9
Wireless LAN IEEE802.11 10
Part 2: IEEE802.11 Overview 12
Wireless IEEE802.11 Standard 13
IEEE802.11 Configurations 14
Wireless LAN Standardization 17
Part 3: Physical layer 18
IEEE802.11 19
AMPLITUDE 20
FREQUENCY 20
Spectrum 21
IEEE802.11a 5GHz PHY Layer 23
IEEE802.11g: Further Speed 24
Extension for the 2.4GHz Band 24
IEEE802.11h: Spectrum and 26
Transmit Power Management 26
… when will 5 GHz WLANs come? 27
PHY Terminology 28
PLCP Protocol Data Unit 29
Part 4: Medium Access Control 30
CSMA/CA Explained 32
CSMA/CA + ACK protocol 33
Station 1 34
Station 2 34
Station 3 34
Station 4 34
“Hidden Node” Provisions 35
IEEE802.11e: MAC Enhancements 36
Contention Free Period 37
Contention Period 37
CFP repetition interval 37
Frame Formats 39
Address Field Description 40
Part 5: MAC layer management 42
Scanning 45
Active Scanning Example 46
Power Management Approach 48
Power Management Procedure 49
MAC Management Frames 50
Part 6: WLAN Mobility 51
IEEE802.11 Ad Hoc Mode 52
Distribution System (DS) 53
ORFDOGLVWULEXWLRQQHWZRUN 54
IEEE802.11f: 55
Part 7: WLAN security 56
• a 40 bit secret key 57
WEP privacy mechanism 58
Shared key authentication 59
IEEE802.11i: 61
Robust Security Network (RSN) 61
Summary: MAC Functionality 63
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VHOIH[SODLQLQJ 65
Probably to consider … 68
Selection of billing method 69
How does it work: 70
Web based access control 70
GSM/GPRS/UMTS 75
WLAN IEEE802.11 75
WLAN – UMTS Interworking: 76
ORJDULWKPLFVFDOH 78
Conclusions for 79
Mobile Network Operators 79
'+&3 82
SMS containing Password 82

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